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Testing the Locked Brummel

Discussion in 'Arborist 101' started by moray, Jul 2, 2008.

  1. moray

    moray AboristSite Guru

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    For a long time I have wanted to test the locked Brummel. Up till now I had considered it to be a useless gimmick, much like the cute little whippings applied to factory-spliced eyes on climbing ropes and split tails.

    What use is it? Does it do something that the standard hollow-braid splice doesn't do? Maybe. If it allows one to make an eye-to-eye split tail that is much shorter than standard, then the answer is yes.

    I just happened to have 100 feet of cheap hardware-store hollow braid, 1/4 inch polypro, that I had used the last couple of years for various tasks. I really hate the stuff; this would be the perfect rope for some destructive tests of the locked Brummel.

    I really wanted to know two things:
    1. in a pull test, where will the rope break?
    2. what part does the buried tail play, if any, in the security of the Brummel?

    I took about 5 feet of rope and spliced a normal eye at one end and a locked Brummel eye at the other. Since a Brummel with a normal-length bury has no advantage over an ordinary splice, I purposely made the first Brummel with a very short bury, the only configuration in which it might have an advantage.

    The photo shows the eye used in the first test.

    [​IMG]

    The red line marks the approximate end of the Brummel section; the bury extends from the red line to the black line.

    I had hardly begun to pull in the first test when the Brummel eye came completely apart. It happened too fast for me to see, but it was clear that nothing broke. The last inch of rope was unravelled, so I surmised that first the tail had pulled out of the rope, then the last inch had unravelled, destroying the "lock", and finally, with nothing holding it, what was left came apart.

    I love an experiment that surprises me; this one did. Even though the Brummel is "locked", there is still significant force trying to pull the buried tail out of the rope. The obvious next step was to repeat the experiment, this time with the buried tail stitched in place.
     
  2. moray

    moray AboristSite Guru

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    After recreating the eye and Brummel, again with a short bury, I put a few stitches through the throat of the bury. This time, when load was applied, both eyes stayed perfectly intact and the rope broke in the middle, far away from either eye.

    The photo shows the results of the test, with the sloppy white stitching clearly visible.

    [​IMG]

    The black mark at the far left indicates, as before, the end of the bury.
     
  3. moray

    moray AboristSite Guru

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    As there was still a fair amount of rope left, I made a normal eye at the broken end so I could run another test on the undamaged Brummel. For this test I removed the white polyester yarn used for stitching, leaving the Brummel eye otherwise untouched.

    Then tension was applied.

    [​IMG]

    Another surprise. The rope broke AND the short bury came out. This confirmed the result of the first test: there is significant force trying to extract the bury even though the Brummel is technically "locked". The red arrow points to the extracted bury. Note that the rope broke right at the end of the bury--the typical breakage point for a hollow-braid splice.

    The small amount of stitching in the second test was clearly necessary to keep the Brummel intact.
     
  4. moray

    moray AboristSite Guru

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    Before proceeding with any further testing, we can already draw a rather sobering conclusion. The locked Brummel is like a parachute. Just as the parachute does nothing until it opens, the Brummel does nothing until the buried part of the splice fails, that is, until it comes apart.

    How good a parachute the Brummel is is not yet clear. When the Brummel does kick into action and support the load, the resulting deformation is severe. I measured the before-testing length of the Brummel in my 1/4" line, from the throat of the eye to entrance point of the bury, at almost exactly one inch. The highly distorted Brummel from the previous break test measures only 3/8" long! This is some serious distortion.

    In saying the Brummel does nothing until the splice pulls apart, I am ignoring the fact that the Brummel does supply some friction tending to prevent this. Even though I am confident that an inch of rope consumed in making a Brummel would be much better spent in making a buried splice, this is an assertion that should be checked by experiment. That is on my short list.

    But the next test will aim to measure the quality of the Brummel "parachute". To do this we need a Brummel where the tail is not buried at all. The photo shows the setup. The locked Brummel has not yet been snugged up to form the finished eye. The tail is very long so as to avoid any possibility of unravelling during the test.

    [​IMG]
     
  5. NickfromWI

    NickfromWI Addicted to ArboristSite

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    Moray- I think you might be off on this one, and I think your posts might be leading people astray. The benefits of the locking brummel (LB) for use in arboriculture are great...as are the cute little whippings! I do think there is a TON of value in the pull tests you are doing, though.

    The locked brummel is about security, not strength. You learned in your first pull test that the LB alone is not adequate to hold the splice together. The tail is indeed part of the splice- but it needs a way to remain intact. Typically this means burying a tail. The tail should be about a fid length, with the taper not starting until about 1/2 fid or a long fid down the tail. That looks like 1/4" or 3/8" rope you're using, so this would be a tail around 5-8" long.

    Another method of keeping the tail intact is to leave it outside, but whip it together a few inches from the brummell. I have done some break testing on these types of splices and found just under an 80% of rope strength. Not good as far as a splice is concerned...but better than almost any knot one might use.

    I have to disagree with your analogy about a LB being similar to a parachute. They are quite different. There are some applications where a rope will sit untouched by man until the day it is retired. I was in a paper mill where they used rope slings that picked up vats of pulp one after the other, about 1 every 3 minutes. Those slings saw impressive loads. They were spliced with straight buries (no LB). No one ever messed around with those slings and there wasn't a chance for the tail to get yanked out.

    Tree work is the exact opposite. Think about any sling one would own. Even when you are not actually using it- it is still getting thrown around, clipped to other gear, etc. Then it might get clipped it to your harness and start climbing around a tree with it. Or a big sling might get pulled off a hook in the truck, carried through the back yard, around the bushes, set on the ground at the base of the tree. All this before it has actually been "used." And all these are chances where something could snag a tail and pull it out. It takes VERY little force (ounces of pressure) to pull a tail out of single braid rope.

    Enter the locked brummel. At those tiny loads- before something bad can happen, the LB holds things together. A whipping can do this, too. I am a bit leery of traditional whipping because we work in a world of cutting tools. All too often chainsaws, handsaws, pruners, loppers, polesaws and more come too close to our climbing gear. It would be too easy for any one of these tools (even a non-running chainsaw) to render a whipping useless.

    Now let's step it up a notch. Let's talk about the rope in use. What is holding that splice together on that huge slings with the straight bury? Well, there are two stages to the load. I will call them pre-compression and compression. Compression is at high loads. The pull on the rope causes the strands to bite down on the buried tail. If you walked up to the splice at full compression, you wouldn't be able to pull the tail out of a straight bury unless you were stronger than the load being applied.

    Before compression happens, we have pre-compression. This is the moment just before the heavy load is applied. Maybe we are talking about 2.5% of the ABS of the rope. I'm not sure the exact number...but it is very low compared to what the rope can handle. During pre-compression, if you got to it in time, you could still pull the tail out of the straight bury.

    Knowing that, let's look at two real-life scenarios. One that happens quickly, and one that happens over time.

    First the quick one. You're climbing on a friction saver (FS) made with a straight bury and no cute little whipping. You throw the FS around the limb, set the climbing line, and begin your descent. What you didn't see is that there is the stub of a twig near your TIP and it is inside the eye of one of the splices on the FS. You get down to a limb and start walking out. As you're doing it, you're pulling your climbing line out at an angle from your TIP. That makes the FS start to rotate around the limb it is wrapped around at your TIP. The little stub from the twig starts pulling sideways on the eye. This pulls the tail out of the splice. You of course were lanyarded in when it happens. You notice it, reset your line and keep climbing.

    The happens-over-time scenario: Climbing on that same FS with the straight bury. That little rope has a MBS of 6,000. At very low loads compression has barely set in. As a rope is repeatedly loaded and unloaded at low loads the tail can creep out a minuscule amount each time. We know that you wouldn't grab the FS in your hand and repeatedly pull and release it a hundred times. That's just silly. But a low...let's say 2.5% load would simulate that. 2.5% of 6,000 comes to 150 pounds. That just lighter than the average climber. You very easily could pull that splice apart inadvertently in a tree without knowing or trying to.

    A proper whipping would prevent the tail from pulling out in both scenarios. The whipping is subject to chafe and snagging though- so keep an eye on it.

    A locked brummel with adequate buried tail that is lightly stitched is place would be near impossible to pull apart in a tree whether on accident or otherwise.

    Each rigging scenario has its own intricacies that may lend itself to different kind of splices. But you're leading people astray when statements like, "the Brummel does nothing until the buried part of the splice fails."

    The brummel is your friend!

    love
    nick
     
  6. moray

    moray AboristSite Guru

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    Nick, thank you for your thorough, thoughtful, and respectful post. This is great stuff!

    I have to say I agree with almost everything you say, but I still view the overall situation somewhat differently. And your point describing how real arborists, in contrast to imposters like myself, may well beat the hell out of their equipment, including their Brummels, is well taken.

    I fully agree, of course. Which is why the rope manufacturers specify stitching the throat to finish and secure the splice. Like you, I am very leery of a whipping, cute or otherwise, for this purpose because it seems much more vulnerable to a cut. Since the integrity of the bury is vital, anyone who abuses their equipment should cover the stitching with shrink wrap or heavy tape. I would probably use blind stitching, myself, if I thought my stitching was vulnerable. Nevertheless, I agree that a Brummel offers a bit of a security against minor cuts, but this comes at a price, which I develop further in the next few posts...

    I have to assume you are describing an unstitched splice. Even then, if we are talking about a standard-length bury, I think this would almost require an engineered jig to pull off, like a smart human with two hands doing their level best to pull it apart. But it is undoubtedly possible. If the throat of the splice is properly stitched, then I will baldly claim it is impossible, for the reason that the stitching effectively applies a significant amount of tension. By the time you have pulled hard enough to break the stitching (hundreds of lbs.), the splice is fully working and no longer vulnerable.

    This is an entirely valid concern, and one I seldom if ever see mentioned. The scenario I play over in my mind involves a huge hawser with spliced eye thrown around a capstan as the ship comes in to the dock. Unfortunately, a drunk smashed into the capstan the previous night, leaving some bruised and roughened metal: consesquently the spliced eye, as the ship continues moving parallel to the dock, catches on this rough stuff and the entire load falls on the buried leg of the eye. It will hold. In my thread on splicing Amsteel Blue, and elsewhere, I tested a ton of hollow braid splices with always the same result: the manufacturer-specified length of bury is many times longer than it needs to be. This is as it should be and must be. They would be crazy to recommend, and we would be crazy to use, splices that would not hold up to very realistic working scenarios, like your stub and my damaged capstan. Not only can you load a single leg of the eye, but you will still enjoy a large safety factor as you do so. My testing (not the last word, by any means!) confirms that their recommendations are extremely conservative.

    Another valid concern, especially in light of the fact that knots are known to creep slowly from repeated load cycles (it has happened to me). Again, the stitching will prevent this.

    Nothing is perhaps a little too categorical. The Brummel certainly does offer a bit of security against a cut. But stitching isn't particularly vulnerable, either (unlike a whipping), and if ever the stitching appears worn or cut, simply restitch. A failure of the stitching does not cause an emergency nor does it cause a failure of the splice.

    I have more data to report, coming up, that bear on the nature of the locked Brummel, and the price tag that comes with it.
     
  7. moray

    moray AboristSite Guru

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    To prepare the Brummel with unburied tail, shown below, an ordinary spliced eye was installed a couple of feet away.

    [​IMG]

    I knew from the earlier tests that the Brummel was going to turn into a compact knot under load. Since I wanted to be very precise about where the rope broke, I paused the test short of the breaking point so I could carefully mark the rope immediately next to the now highly compressed Brummel. Then I went ahead and added tension till the rope snapped. The result is shown below.

    [​IMG]

    The photo clearly shows the standard eye at the bottom, looking as good as new, whereas the rest of the rope looks like it has been ground up by a tornado. A closeup of the break is shown below.

    [​IMG]

    The rope did break at my mark, as expected. This would have been a point in which the rope was under full tension, yet severely squeezed by the overstressed Brummel. In other words, the failure mode was just the same as any ordinary knot.

    The next experiment will test the friction characteristics of the Brummel. Does an inch of Brummel hold as well as an inch of ordinary buried splice?
     
  8. moray

    moray AboristSite Guru

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    When you make a locked Brummel you are using up valuable rope length that could, instead, be part of a normal buried splice. The idea of this experiment was to compare the holding power of a Brummel-style splice with a normal bury splice. A non-locking Brummel of 5 tucks was created. The length of the Brummel was carefully measured, then a non-tapered bury splice was made a short distance away. The length of the bury was exactly the same as the length of the Brummel.

    [​IMG]

    When the rope was pulled to failure, it broke at the Brummel. The Brummel after the test had only 4 tucks, so apparently one of the tucks slipped out before the rope broke.

    This didn't seem a very conclusive result to me, so I ran another test. This time the Brummel had 3 tucks, and, as before, the bury in the other splice was exactly the same length (2 inches) as the Brummel. The rope was pulled to failure. This time the rope did not break, but the Brummel came apart. The standard splice was unscathed.

    This seems to show rather convincingly that, inch for inch, a buried splice has more holding power than a Brummel.
     
  9. pdqdl

    pdqdl Not old enough yet to know better

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    YES ! Some years back I was using a safety lanyard that I had spliced myself (double braid, both inner and outer core were buried in opposite directions) and I foolishly didn't think that I needed to sew them in together.

    About 25' up a walnut tree, not tied in, I got a funny feeling about my lanyard, right before I used it. When I checked it, it fell apart in my hands! I was using a double ended safety, so I was still attached to the tree, but I was moments away from disconnecting the secure end and relying on the splice that failed. A small amount of luck less, and I would have surely fallen to a certain injury.

    Needless to say, I am in full support of Moray and his splicing posts. So far, I have not gone back up on one of my splices unless it was sewn in, in addition to being made well otherwise.
     
  10. moray

    moray AboristSite Guru

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    Some Thoughts and Conclusions

    With some real data in the bank, it's time for the other fun part, the conclusions. Let's summarize what we know:

    1. The Brummel is not complete by itself. The tail is never left flapping in the breeze, but is buried in the standing rope. That is, the Brummel is always combined with a normal buried splice.
    2. Though it is called a "locked" Brummel, it does not lock the splice in place or prevent the splice from pulling apart (though it does help somewhat). What "locked" means is that if the splice pulls completely apart, the Brummel won't also pull apart, but will lock up into a very tight knot, keeping the eye intact.
    3. When the Brummel, in emergency use, is forced to take the entire load because the splice has come apart, it will fail just like a knot does when the load becomes excessive.
    4.Though the Brummel, in normal use, does supply some holding friction in the same way that the splice does, inch for inch it is less effective than the splice.

    It is helpful and accurate to think of the Brummel as a peculiar emergency knot. In ordinary use it isn't a knot at all, but a short stretch of second-rate splice. This is the only form it will ever take, except in some vanishingly small number of cases (I've never heard of one) in which the splice comes apart. Then, chameleon-like, it transforms into a very tight knot. This is its real purpose, to be a safety knot in waiting, automatically deployed when the need arises.

    What is this emergency parachute actually worth? Even if you have agreed with me up to this point, we may still disagree on the value of the Brummel because it is a largely psychological question. I think the likelihood of a properly made hollow-braid splice coming undone is exactly nil, so I don't go to the extra work of backing up my splices with a Brummel. What's more, if I did think I was using an unsafe splice, I would not be inclined to back it up with a knot (Brummel); I would simply replace it with a knot (a good knot, not a Brummel). Why go to all the work to make both a splice and a knot to get something only as good as the knot?

    In any event, my purpose in doing these experiments was to reveal something about the actual behavior of the locked Brummel, not to persuade anyone to use them or not.

    Since there are thousands, maybe hundreds of thousands of slings, split tails, and whatnots out there with locked Brummels, is there anyone out there that knows of a splice coming apart and being saved by the Brummel?
     
  11. NickfromWI

    NickfromWI Addicted to ArboristSite

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    Agreed.

    I disagree 100%. The LB does lock the splice from pulling apart in low or high load applications. It prevents the rope/splice from slipping.

    Straight bury will also fail when forced to take the entire load. Anything will eventually fail.

    It depends on what your goals are. If you are concerned about maximum efficiency, then go for a straight bury. If you want security, do the LB.

    The LB is more efficient than a standard knot. It is much more compact than any knot, AND it allows shorter buries than a standard straight bury.

    No- that is the whole point.

    The tail won't come apart if it is buried. The compression of the outer strands holds the inner tail together, which in turn holds the entire LB together. For the splice to fail, the whole rope has to fail. Anyone with the flick of the wrist can make the straight bury fail. You can't do that with the LB.

    What size rope are you using? Test it with a short buried, tapered tail...say 2 or 3 inches with the rope you are using. Then test a straight bury with a 2 or 3" tapered tail.

    Also- you should do testing with new rope. Defects in used rope can lead your testing astray.

    love
    nick
     
  12. moray

    moray AboristSite Guru

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    Good! We have a discussion going.

    Let me make a couple of general comments before diving into the details. My motivation for experimenting with the LB was partly just to collect some real data on its behavior, and partly to see if my skepticism about its usefulness was justified. Thinking back on it, I realize my little experiments, since they did not reveal any gross defect in the LB, shed no light at all on the second question.

    It is always good to have someone challenge your ideas and force you to cross your t's and dot your i's. After studying your latest comments, I think our differences are more apparent than real, and less about facts than the significance we attach to them. On to the details...

    I think this must be an apparent disagreement. I know you have made a million of these splices, and you know that the splice, until it is stitched, can be easily pulled apart by hand, just like a standard splice. That's all I was saying. Admittedly, the LB does limit how far a splice without stitching could potentially slip in actual use, in principle somewhat less than the length of the LB. This would mean that for almost any LB/splice combo anyone would ever use, the core of the splice would never pull all the way out--a good thing. It seems to me it would be more accurate to say the LB limits any slippage in the splice, but doesn't lock it. The stitching does that.

    This a big and very interesting subject, and one I am actively working on, but it is not really about the LB. I have tested this in various configurations and have always found, even with substandard bury lengths, that the core does not pull out as long as the throat or entry point is stitched. But this is all preliminary and a bit off subject.

    I do agree with this, but I think some clarification is needed. I don't know what you mean by "efficient", but I agree that the LB is as compact as you can get. As to allowing shorter buries, I will readily concede that the LB offers security in the case of a very short bury. But I think phrasing it the way you did could be a bit misleading because your wording seems to imply inserting the LB is a 100% positive thing. Not to belabor the point, but the LB is often stuck in there when space is limited; the space it takes up is subtracted from the bury that would otherwise be there. It seems a bit peculiar to describe this situation as "allowing" a shorter bury. You could equally well say it "requires" a shorter bury if you are going to use it. You have to give up some precious bury length to use the LB, making it more likely that the now shorter splice actually will fail. On the good side, as we both agree, the LB will protect you against such a failure.

    My skepticism about the LB applies to the case where the bury is not short. Here the issue is cost vs benefit, and on the benefit side a lot of judgment and guesswork comes into play. On the cost side is the extra labor and material to make the LB compared to the straight splice. On the benefit side is security against the (stitched) splice coming apart. The various mechanisms by which this might happen all hinge on somehow getting a large load entirely on the buried core, and then assuming that this would cause the splice to slip. It is extremely difficult, even intentionally, to put the full load on the core, so the scenarios where this could happen by accident seem highly implausible to me. Even if this did happen, the likelihood that this would then pull the splice apart also seems extremely low. Put those two together and you have something so wildly improbable that it is not worth considering.

    Others may assess this differently, of course. I will say again, so no one misreads my meaning, that I am in no way criticizing or questioning the efficacy of the locked Brummel; I think it works exactly as advertised. I am questioning whether it is worthwhile to add the LB to a full-length standard splice. My confidence in the standard splice is so high I think the answer is no.
     
  13. allene222

    allene222 New Member

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    This is rather an old post but hits high on Google so I wanted to add a few comments. I have done stress to failure testing using Amsteel using both a locked Brummel and a standard bury splice stitched. Neither one failed. The Amsteel broke in the middle between them. I think it is pretty well agreed that a Brummel is used to keep the splice together before a high load is applied. It should not part of the strength of the splice. Without a Brummel or stitching, you can just pull the splice apart with an easy pull. Something needs to hold it together before the strands lock around the bury. In my experience, either a brummel or a stitched simple bury are equally strong and stronger than the line they are made on so it really doesn't matter "how strong" they are. The difference for me is that I find the Brummel easier to do than the stitching. It is also easier to undo. I wrote up a detailed HOW-TO on making a Brummel and offer it for anyone interested: Brummel Eye Splice If you want to see the testing I did, look on the page with the Soft Shackle section. Cheers,

    Allen
     
  14. TreeLogic

    TreeLogic ArboristSite Member

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    Dear NickfromWI,
    I know that you know your stuff when it comes to splicing. And I feel Moray does as well. My question here is as a curious novice, and by no means a disagreement to anyone.

    I've seen your video on aluminum rings, where you create a friction saver from the core of another rope. You don't use locking brummels on your eyes around the rings, but instead do a straight bury with lockstitching. Why is this acceptable here, but not on an i2i tail? Possibly too thick of a cord and/or length of the finished product?

    In all honesty, as far as looks go, I'll take the straight (stitched) bury any day. I would say it's easier too.

    Thanks, Will
     
  15. Grace Tree

    Grace Tree Impossible Access

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    I don't think Nick has been on here for a couple of years. You might try the other forum.
    Phil
     
  16. TreeLogic

    TreeLogic ArboristSite Member

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    OK. Thanks Phil.
     

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